The present invention relates to a method of reserving resources in a packet network. It has particular utility in relation to providing an internet offering Quality of Service guarantees.
Methods of reserving resources in an internet are well known. The method which is currently best supported in the Internet is that defined by the Resource Reservation Protocol (RSVP)
There is a desire to enable an internet to provide real-time communication as is, for example, required if telephone conversations or video-conferences are to be conducted over it. In this regard, two qualities of service that might be provided have been specified by the following documents (which are incorporated herein by reference):
(1) S. Schenker, C. Partridge, R. Guerin. Specification of Guaranteed Quality of Service, Request For Comments, September 1997, RFC 2212; and PA1 (2) J. Wroclawski. Specification of the Controlled-Load Network Element Service, Request For Comments, September 1997, RFC 2211. PA1 (3) P. White. RSVP and Integrated Services in the Internet: a tutorial, IEEE Communications magazine, May 1997. PA1 operating a plurality of receiver hosts to send reverse-routed packets, containing one or more reservation influencing parameters, along a route via one or more of said interconnecting nodes to one or more sender hosts; PA1 operating said one or more intermediate nodes to: PA1 update said parameters to represent the highest quality of service class requested by downstream receivers; and PA1 reserve resources in accordance with the resource reservation process associated with said highest quality of service class. PA1 means for combining one or more parameters of received reverse-routed packets to generate combined reservation influencing parameters; PA1 means for storing said combined parameters; PA1 means for sending a reverse routed packet containing said combined parameters further along said route to said sender hosts; and PA1 means for reserving resources in accordance with combined reservation influencing parameters stored at that node responsive to a reservation packet.
Essentially, Guaranteed Service as defined in the first document allows a user to specify an upper bound on the time taken for his message to reach a recipient, whereas Controlled Load Service offers a service qualitatively similar to that provided by the internet when it is only lightly loaded. Operating an internet in accordance with the RSVP protocol allows the provision of real-time communication. The provision of such communication to the above-mentioned Quality of Service classes when operating an internet in accordance with the RSVP protocol is discussed in the following document (also incorporated herein by reference):
In an internetwork operating in accordance with the RSVP protocol, a sender which wishes to increase the level of traffic it is sending to one or more receivers first sends out a path information packet which contains information concerning the characteristics of the path along which it has travelled and also information specifying the increased traffic level. This passes through each of the nodes through which the sender's increased traffic will pass in travelling to the one or more receivers. Path characteristic data is installed at those nodes as a result of the packet passing through them. Once this process is complete the one or more receivers calculate a required reservation on the basis of the increased traffic specification and end-to-end path characteristics (obtained from the received path information packet) and send a packet back towards the sender specifying the reservation required. Provided sufficient network resources are available each node receiving the reservation-requesting packet reserves appropriate resources and forwards the packet back towards the sender.
When an internet is operated in accordance with RSVP, receivers are responsible for requesting the reservation of resources. In contrast, in an internet operating in accordance with the Internet Stream Protocol Version 2 (ST2), senders are responsible for requesting reservation of resources.
Although a network operating in accordance with ST2 allows resources to be reserved more quickly than is possible with RSVP, it does not allow for different levels of service to be provided in relation to a single one-to-many or many-to-many communication.